Vancomycin resistant enterococci (VRE) represents a serious problem for healthcare worldwide. For example, the Center for Disease Control (CDC) has released data for antibiotic resistance associated with hospital-caused infections from January 1989 to March 1993, showing a 20-fold increase in the percentage of enterococci that were resistant to the antibiotic vancomycin (MMMWR 42:597-599, 1993) during this period. Both vanA and vanB genes of enterococci have been found to be associated with the increased resistance.
Transfer of the vanA and vanB antibiotic resistance genes to non-enterococcal species is also a growing concern. The vanA gene has been found in Corynebacterium, Arcanobacterium and Lactococcus species (Power et al. J. Antimicrobiol. Chemother. 36:595-606, 1995). Recently, Poyart et al. (Antimicrobiol. Agents Chemotherap. 41:24-29, 1997), reported an occurrence of a Streptococcus bovis clinical isolate with a VanB resistance phenotype. The gene was shown to be highly homologous to the prototype vanB gene from Enterococcus.
Increased use of antibiotics has resulted in the emergence of vancomycin-resistant microorganisms such as Enterococcus spp. and Staphylococcus spp. (Dutka-Malen et al., Antimicrobiol. Agents Chemother. 34:1875-1879, 1990). Vancomycin-resistant S. aureus (VISA) is certain to emerge in hospitals with high rates of methicillin resistant Staphylococcus aureus (MRSA) and the use of vancomycin (Edmond et al., Ann. Intern. Med. 124:329-334, 1996). Recently, VISA isolates have been reported in Latin America (Navarro Marin, International Journal of Antimicrobial Agents 7:293-294, 1996).
Briefly, there are four phenotypes of enterococci that can be separated based on expression of constitutive and inducible resistance of the glycopeptides, vancomycin and teicoplanin (Leclercq and Courvalin, Clin. Infec. Dis. 24:545-556, 1997). Inducible resistance to high levels of vancomycin (MIC.gtoreq.64 mg/l) and teicoplanin (MIC.gtoreq.16 mg/l) is characteristic of the VanA phenotype. This type of resistance is plasmid mediated. The vanA gene has recently been found on mobile elements that can direct their own transfer from the chromosome of one Enterococcus strain to another. The VanB phenotype is described as inducible resistant to vancomycin with MIC of 4 mg/l to .gtoreq.1,000 mg/l but displaying susceptibility to teicoplanin. The vanB gene is transferable by conjugation in certain strains. The genes in the VanC phenotype produce constitutive resistance and occur in E. gallinarum and E. casseliflavis and E. flavenscens (Leclercq and Courvalin Supra; Navarro & Courvalin, Antimirobiol. Agents Chemother. 38:1788-1793, 1994). Recently, VanD phenotype has been reported and is characterized by moderate levels of vancomycin resistance and low level resistance to teicoplanin (cited in Leclercq and Courvalin Supra).
The majority of conventional methods for detection of glycopeptide resistant enterococci have drawbacks related to time, lack of specificity and sensitivity of detection. For example, detection of the glycopeptide resistant enterococci can be carried out by conventional susceptibility testing (broth and agar methods), but these techniques are slow, and automated detection is not recommended due to poor performance (Aarestrup et al., Antimicrob. Agents Chemother. 40:1938-1940, 1996). Although the above methods can be used to detect VRE, there is an urgent need for a rapid, user friendly and reliable method for detecting the vanA gene and vanB genes from VRE, both in the hospital and community settings. The present invention provides probes and methods for detecting the vanA and vanB genes rapidly. Further, the present invention provides other related advantages.